1. Field of the Invention
The present invention concerns a process for producing vinegar which comprises subjecting cereals or fruits as the starting material to alcohol fermentation, removing high molecular weight substances from alcohol fermentation products by treating the fermentation liquids by way of ultra-filtration membranes and then subjecting them to acetic acid fermentation.
2. Description of the Prior Art
In the production of vinegars, liquid filtrate obtained by primary filtration of fermentation products (hereinafter referred to as Moromis) after the completion of acetic acid fermentation have been filtered by using ultra-filtration membranes with the fractional molecular weight less than 50,000 thereby preventing the occurrence of secondary precipitation, preventing turbidity in the products and reducing the change of coloration (refer to Japanese Patent Application Laying Open No. Sho 61-242572).
Also, in the field of Sake and Soy sauce (Shoyu), a method has been known for the purification and filtration using ultra-filtration membranes in the final filtration. This method is applied for removing proteins that cause precipitation (Japanese Patent Publication No. Sho 60-23823).
Generally, alcohol Moromis obtained from cereals as the starting material contain high molecular weight substances, which cause bubbling in the aerated acetic acid fermentation and, further, cause precipitates during preservation of vinegar products after acetic acid fermentation.
According to the conventional production process for vinegar as described above, Moromis after the completion of the acetic acid fermentation are filtered by using ultra-filtration membranes with the fractional molecular weight of less than 50,000 thereby preventing occurrence of secondary precipitation, preventing the turbidity in the products and reduce the change of coloration. However, according to the prior art method, it can not prevent bubbling during aerated acetic acid fermentation. Then, although defoamers have generally been used for suppressing the bubbling in the aerated acetic acid fermentation, the defoaming effect obtained by this method is only temporary and not quite satisfactory.